Asymmetric beam spotlight

ABSTRACT

An optical system comprising a light source and an asymmetric reflector for producing a noncircular beam of light having a generally oval cross section and wherein the intensity and angular extent of the beam are variable by moving the source axially with respect to the reflector. The reflector is defined by a continuous, asymmetric surface generated by a curve v f(u) in a meridian plane thereof, which curve varies angularly in successive meridian planes through an angle phi about a moving point (Ro, theta ,Zo) fixed with respect to the curve in each meridian plane and falling on a circle concentric with and in a plane normal to the optical axis Z of the reflector. The angular variation phi is described by the relation phi g ( theta ) and conforms to the restriction that phi is continuous and periodic on theta 2 pi , where angle theta describes the angular position of the meridian plane about the optical axis of the reflector.

United States Patent 1191 Levin Aug. 21, 1973 ASYMMETRIC BEAM SPOTLIGHT[75] Inventor: Robert E. Levin, Hamilton, Mass.

[73] Assignee: GTE Sylvauia Incorporated,

Danvers, Mass.

[22] Filed: May 30, 1972 [21] Appl. No.: 257,938

[56] References Cited UNITED STATES PATENTS 1/1970 Yamaguchi et al240/4l.37 X 7/1961 Motter 240/44.2

Primary ExaminerSamuel S. Matthews Assistant Examiner-Richard M. Sheer Attomey-Norman J. OMalley, Edward J. Coleman et al.

[ 5 7] ABSTRACT An optical system comprising a light source and anasymmetric reflector for producing a noncircular beam of light having agenerally oval cross section and wherein the intensity and angularextent of the beam are variable by moving the source axially withrespect to the reflector. The reflector is defined by a continuous,asymmetric surface generated by a curve v f( u) in a meridian planethereof, which curve varies angularly in successive meridian planesthrough an angle (I: about a moving point (R,,,0,Z,) fixed with respectto the curve in each meridian plane and falling on a circle concentricwith and in a plane normal to the optical axis Z of the reflector. Theangularvariation d) is described by the relation g (0) and conforms tothe restriction that 1b is continuous and periodic on 0 2n, where angle0 describes the angular position of the meridian plane about the opticalaxis of the reflector.

7 Claims, 7 Drawing Figures Patented Aug. 21, 1973 3,754,134

- 2 Sheets-Sheet 1 FIG.2

Patented Aug. 21, 1973 3,754,134

2 Sheets-Sheet f;

INTENSITY-I03 CANDELA ANGLE FROM Z ASYMMETRIC BEAM SPOTLIGHT BACKGROUNDOF THE INVENTION This invention relates to spotlight projectors and,more particularly, to projectors in which the light beam is noncircular.and the beam size is variable.

Spotlight projectors are widely used in a number of fields, includingthe theatre, still photography, motion pictures, and television. In suchapplications'it is desirable to provide an asymmetric beam shape, whichdeparts from a circular, axially symmetric intensity distribution, forvarious purposes, suchasmatching the aspect ratio of associatedcameras.The beam angle may be fixed, or it may be desired-to vary itthrough'a'con siderable range of angles; for example, a 2:1 variation"or greater. 2

Asymmetric. beam patterns have been produced by many techniques. The useof'a Ienticular refractor; such as employed on headlight lamps,generally is un'- desirable for spotlights due to cost, weight and heattrapping. Asymmetric beam patterns are produced'by reflectors ofrevolution with asymmetric oriented sources such as the classic bow tiepattern of a pa-- raboloid with a cross-axis incandescent filament. Theintensity distribution of such a system, however, is not arbitrarilyvariable to match an a priori' intensity distri-' bution. 7

Many asymmetric reflectors are known. A principal known form comprisesreflector sections of various specific shapes and orientations butfabricated as a single integral reflector, with each-section productinga beam. These individual beams overalp in a prescribed manner to formthe total asymmetric spotlight beam, as exemplified by U.S. Pat. No.3,331,960, assigned to theassignee of the present application. Sinceindividual components of thebeam each depend on the relation of sourceto reflector section orientation, this system' is very sensitive tomechanical tolerances. Diffusion, such' as etching the reflectingsurface, will reduce this sensitivity but, at the same time, reduce thecontrol of the light.

SUMMARY OF THE INVENTION Accordingly, it is an object of the presentinvention to provide an improved asymmetric beam spotlightunit having areflector which is particularly suitable for variable beam applications.

Another object of the invention is to provide an asymmetric beamspotlight having a reflector of more simplified design, which enablesmore relaxed manufacturing tolerances, and which is suitable for usewith a movable light source.

A further object of the invention is to provide a reflector for anasymmetric beam spotlight which provides more efficient use of thegenerated light.

In accordance with the invention, I have'discovered a particular form ofasymmetric reflectorin which'continguous sections of the reflectivesurface contribute luminous flux to contiguous regions of theilluminated field, and in which a small displacement of the luminoussource primarily produces a displacement of the light beam as a wholewithout significantly changing the relative distribution of light fluxwithin the beam. As a result, small changes in the light sourceposition, light source aspect ratio, reflector surface contour, and thelike, that comprise normal manufacturing and production tolerances, willnot produce different effects on different parts of the light beam withthe consequence of large changesof the spotlight intensity distribution.This invention produces a beam that is generally describ'ed'as oval,andthe design concept is directly related'to'the resulting beam oflight. The design constraints on the shape of the reflecting surface arecompatible with the most practical techniques of precisely formingthereflectors.

BRIEF DESCRIPTION OF THE DRAWINGS This invention'will bemore fullydescribed hereinafterin conjunction'with the accompanying drawings, inwhich:

FIGS; 1 and 2 are front and side views, respectively, of'a reflectoraccording to the invention;

FIG. 3' shows a series of curves representing respectively identifiedmeridian plane sections of the reflecting surface of FIG. 1,

FIG. 4 is a generalized graphical-illustration of the mathematicaldescription of the reflecting surface of FIG. 1;

FIG. 5 is'a schematic representation of a particular embodiment of aspotlight unit according to the invention, with the reflectorillustrated by a'single meridian section;

FIG. 6'is a schematic front view of the total reflector at plane'9 ofFIG; 5; and

FIG. 7 shows the intensity distribution produced'by the reflector ofFIG; 5.

DESCRIPTION OF PREFERRED EMBODIMENT The general form of a concavereflector'according to the invention is shownin FIGS. land 2. Thereflecting surface 1 is continuous and asymmetric with respect to theoptical axis Z, and can'be produced by many fabrication techniques, atypical one of which is hydroforming.- Other suitable methods ofmanufacture include stamping, high velocity forming, deep drawing,electromagnetic forming, and electrodeposition. The reflector may beadapted for mounting byany convenient manner, for example by a flange 2,which may be formed as an' integral part of the reflector. At the backof the reflector, concentric with its optical axis Z, a hole 3 isprovided through which a light source may be introduced into thereflector.

Representative meridian plane sections of reflecting surface 1 areillustrated by the curves of FIG. 3, respectively identified as taken onlines A, Band C of FIG. 1.

The mathematical fonn of the reflector will now be describedwith'reference to FIG. 4. A specific curve 4, v =flu), is defined on arectangular coordinate system (u,v). A cylindrical coordinate system(R,0,Z) is established for the reflector where the Z-axis is the opticalaxis of the reflector. The (u,v) coordinate system always lies in ameridian plane, i.e., it contains the line R 0. One point P, having thecoordinates (u,,,v,) in each meridian plane, bears a fixed relation tothe curve 4 for all meridian planes, namely, it coincides with the point(R 0,2,) of the cylindrical coordinate system which generates a circularlocus'in three dimensions as 0 varies. Thus, point P is a moving pointfixed with respect to curve 4 in each meridian plane and falling on acircle concentric with and in plane normal to the optical axis Z.

In a preferred form, R, O is in the vicinity of the light source, butthis is not a necessary condition to the principles of the invention.

The (u,v) coordinate system rotates about point P, as described by angle4) between the lines v O and R O, as the meridian plane rotates aboutthe optical axis Z. Specifically, the relation is (b =g(), where theangle 9 describes the angular position of the meridian plane about theoptical axis. Hence, as the reflecting surface is generated by the curve4, said curve moves angularly in successive meridian planes throughangle (1 about the moving point P. in accordance with the invention,however, this angular variation must conform to the restriction that d)is continuous and periodic on 0 21r.

If the intensity distribution is required to possess symmetry about twoorthogonal planes containing the optical axis, nominally the horizontaland vertical planes, :1) is made an even function about 6 O and 8 17/2.The reflector is formed by a section of this generated surface. in thepreferred form the front of the reflector is in a plane normal to theoptical axis, specifically, by cutting the generated surface by theplane Z 2,. It is preferred to provide an opening for the light sourceon the axis of the reflector. This may be done by cutting the generatedsurface by plane Z Z The principles and teachings of this inventionapply equally well if the front of the reflector is defined in any othermanner or if the light source is introduced into the reflector at someother location.

The selection of the functions v =f(u) and 0 g(0) depends on therequired intensity distribution and the form of the light source. Theselection can be made by any of the techniques well-known to thoseversed in the art of reflector design. When the light source dimensionsare small with respect to the reflector dimensions or when only thedimension parallel to the optical axis is large, the complete designprocess is simplified since each meridian plane section of thereflecting surface principally affects the intensity distribution inthat same meridian plane. With these light source conditions, the spreadof luminous flux in the sagittal plane for an element of the reflectingsurface is small since the angular sagittal subtent of the source withrespect to the reflector element is small. Techniques are well known,but more complicated, for other source forms.

Reflectors of a generally oval appearance have been made in the past,but they do not conform to the form and restrictions of this invention.Generally, these have been defined by reflector cross-sections invarious parallel and/or orthogonal planes or defined by various conic orhyperconic equations. None of the oval reflectors under prior artconform to the relation between meridian plane sections as prescribed bythe: present invention.

In addition to permitting simple designs of asymmetric beam spotlights,this form of reflector possesses another singular advantage. It issimple to manufacture compared to other asymmetric forms. A singletemplate representing the generating curve 4 controls the matching of aforming tool along the reflector surface in a meridian plane, i.e., aplane of constant 0. As succeeding profiles of the forming tool aremachined, the template is rotated (da is varied) as a function of thedisplacement of the meridian plane. This procedure permits a singleplanar curve to be used to develope an asymmetric 3-dimensional surfacein a manner analogous to the well known use of a planar curve fordeveloping a surface of revolution.

A specific embodiment of this invention is schematically represented inFIG. 5. This spotlight produces a photographically defined 26 X 34 beamto match the aspect ratio of specific camera formats. This is a moreefficient utilization of the generated luminous flux than provided by acircular beam. The device operates at about two-thirds of the power ofpreviously employed spotlights capable of performing the same function.The generating curve at =f(u) is defined in two sections as M:(0.2923714 0.95630v) 1.9126014 0.58474v l and N: (0.12187u 0.9925511.985l0u 0.24374v 1 (dimensions in inches) The point P of r0- tation forthe (u,v) coordinate system is u, v, O and R, Z =0, point 5 of FIG. 5.The source 6 is a coiledcoil CC-8 filament of a tungsten halogenincandescent lamp 7 supported within or in immediate proximity to thevolume defined by the reflector surface and the aperture plane of thereflector. The axis of the secondary helix is coincident with theoptical axis of the reflector (R O). The overall helix length isapproximately 0.375 inches, and the outer envelope of the helix has adiameter of approximately 0.133 inches. The helix is nearly centered onpoint 5, with the exact location being selected for the desired beamspread. Axial motion of this filament changes the beam spread andmaximum intensity while maintaining the approximate angular beamdivergence ratio of 26:34 over a photographically useful range. Theaxial motion can be provided by a screw 8 or by any other mechanism thatgenerates linear motion.

The front of the reflector is defined by the plane Z 1.6262, identifiedby the numeral 9. The relation d: g(0) necessary to complete thespecification is most easily visualized by an indirect specification.The front reflector aperture 10 in plane 9 is shown front view in FIG.6. The (u,v) coordinate system is rotated through the angle (1; suchthat section M of the generating curve always intersects the closedcurve 10. Curve 10 is defined by R 1.48000 0.11755 sinO) The resultingintensity distribution of this particular embodiment of the inventionusing a 3,400 K incandescent filament is shown in two orthogonal planesin FIG. 7. The normal horizontal plane is 0 11/2, and the normalvertical plane is 6 0. The surface finish of the reflector isessentially specular but with a slight macroscopic roughness. Thisprevents a general diffusion of the light but smooths the beamirregularities due to the convolutions of the filament.

What I claim is;

l. A spotlight unit for producing a beam of noncircular and generallyoval cross section comprising, a concave reflector defined by acontinuous surface asymmetric with respect to its optical axis Z, saidreflector having an aperture in a predetermined plane, and a lightsource supported substantially within the volume defined by saidreflector surface and the aperture plane thereof, said reflector surfacebeing generated by a curve v =flu) in a meridian plane section thereof,said curve moving angularly in successive meridian planes through anangle :1) about a moving point P fixed with respect to said curve ineach meridian plane, said point P falling on acircle concentric with andin a plane normal to the optical axis Z of said reflector, and saidangular variation 4: being described by the relation 4 g(9) andconforming to the restriction that 41 is continuous and periodic on 0211-, where angle 6 describes the angular position of the meridian planeabout the optical axis Z of said reflector.

2. The spotlight unit of claim 1 wherein said light source is anincandescent filament.

3. The spotlight unit of claim 1 in which said light source is movablein an axial direction with respect to said reflector for changing theangular spread of said beam.

4. The spotlight unit of claim 3 wherein said light source is anincandescent filament.

5. The spotlight unit of claim 1 wherein said reflector is defined bythe generating curve described by (0.2923714 0.95630v) 1.9l260u 0.58474v1 and (0.l2l87u 0.99255v) 1.985l0u 0.24374v l as two sections, and saidgenerating curve motion g(0;) is described parametrically byconstraining the curve to intersect the closed curve defined by Z 1.6262and R l.48000(l 0.11755 sin 0) in the cylindrical coordinate system(R,0,Z), with the point P defined as 14 v, O and R Z, O.

6. The spotlight unit of claim 5 in which said light source is movablealong the optical axis of said reflec tor for changing the angularspread of said beam.

7. The spotlight unit of claim 6 wherein said light source is anincandescent filament.

1. A spotlight unit for producing a beam of noncircular and generallyoval cross section comprising, a concave reflector defined by acontinuous surface asymmetric with respect to its optical axis Z, saidreflector having an aperture in a predetermined plane, and a lightsource supported substantially within the volume defined by saidreflector surface and the aperture plane thereof, said reflector surfacebeing generated by a curve v f(u) in a meridian plane section thereof,said curve moving angularly in successive meridian planes through anangle phi about a moving point P fixed with respect to said curve ineach meridian plane, said point P falling on a circle concentric withand in a plane normal to the optical axis Z of said reflector, and saidangular variation phi being described by the relation phi g( theta ) andconforming to the restriction that phi is continuous and periodic ontheta 2 pi , where angle theta describes the angular position of themeridian plane about the optical axis Z of said reflector.
 2. Thespotlight unit of claim 1 wherein said light source is an incandescentfilament.
 3. The spotlight unit of claim 1 in which said light source ismovable in an axial direction with respect to said reflector forChanging the angular spread of said beam.
 4. The spotlight unit of claim3 wherein said light source is an incandescent filament.
 5. Thespotlight unit of claim 1 wherein said reflector is defined by thegenerating curve described by (0.29237u + 0.95630v)2 1.91260u -0.58474v + 1 and (0.12187u + 0.99255v)2 1.98510u - 0.24374v + 1 as twosections, and said generating curve motion phi g( theta ) is describedparametrically by constraining the curve to intersect the closed curvedefined by Z 1.6262 and R 1.48000(1 + 0.11755 sin2 theta ) in thecylindrical coordinate system (R, theta ,Z), with the point P defined asuo vo O and Ro Zo O.
 6. The spotlight unit of claim 5 in which saidlight source is movable along the optical axis of said reflector forchanging the angular spread of said beam.
 7. The spotlight unit of claim6 wherein said light source is an incandescent filament.